The present invention relates to a squeegee structure for a screen printing frame and which is built into a printing station of a screen printing machine. The squeegee mountings, together with the squeegee of the arrangement, is held on the printing material supply side of the printing screen by means of a number of thrust piston drives so that they may be raised and lowered. The drives are distributed over the printing area, activated by a pressure medium, and braced by a squeegee support at the printing station.
There are known squeegee arrangements for planar and for rotational screen printing machines in which squeegee supports are mounted at the printing stations, with a number of thrust piston drives activated by a pressure medium being fastened to the supports. The thrust piston drives are designed either as single acting or double acting cylinder-piston units, whose piston rods are connected with each other by a squeegee extending the width of the printing area.
Since the squeegee must be pressed with a certain force against the printing material supply side of the screen stencil, the thrust piston drives must be braced against the squeegee support. This causes the support to bend. The support may not be made as stiff as desired because of the generally limited available space. The arrangement of the thrust piston drive is such that a similar bending of the squeegee mounting is avoided. However, it is unavoidable that the piston thrust drives follow the bending of the support or carrier frame, with the result that the piston thrust drive can become misaligned and seized.
The piston thrust drives can be so designed that they lift the squeegee off the screen upon interruption of the printing operation. For simply operating piston-cylinder units, a spring is included therein for this purpose. The spring is under load during the printing operation and, when the operation is discontinued lifts the piston with piston rod and the squeegee holder attached thereto from the screen stencil.
For cylindrical stencils printing screens, it is necessary in changing the silk screening screen that the squeegee structure penetrating the inside of the screen printing stencil be disassembled. Only then can the screen be replaced by another.
The object of the invention is to devise a squeegee structure of the type described above which prevents seizing of the piston thrust drive caused by bending of the thrust drive support, without, however, having to sacrifice thereby the advantage of easy removal and replacement of the squeegee structure.